This invention relates to a controlling apparatus to obtain an intended exact amount of materials by using a flow mater or a weight measuring scale.
In a batch measuring system where liquid reserved in a vessel such as stock tank is fed into a preparation vessel by a intended amount to be obtained (hereinafter referred to simply as intended amount) through a feed line of tube with a stopping valve, pre-set amount value, so-called overrun, defined as an amount to be fed after the system generates a signal to stop the valve is estimated in advance before starting the feeding and the value is stored as a fixed one in memory, and after starting feeding, a signal for stopping the valve is generated when a total fed amount PV reaches the value (Axe2x88x92Vpr), wherein A is a intended amount and Vpr is the pre-set amount.
To shorten the measuring time for obtaining the intended amount, the system usually has main feed line with a larger diameter tube and valve and bypass feed line with a smaller tube and valve. At starting feeding both feed lines are used to make a higher flow rate and the larger diameter valve is closed to make the flow rate slow down when the total fed amount PV reaches the value (Axe2x88x92B): wherein A is a intended amount and B is an alerting amount. The alerting amount is an appropriate amount to determine the timing to shift the feeding rate from high to low because generally low feeding rate is easier in accurately controlling the feeding amount than high feeding rate. If the timing is too early, it will take a long time to obtain the intended amount because the large diameter feed line is closed too early. Thus the alerting amount is determined as relatively very small amount taking total feeding time and control accuracy into consideration.
However, if a value of the intended amount is close to the alerting amount value, i.e. a very small amount, the shift of the feeding rate from high to low is caused immediately after starting feeding at high feeding rate. It may end up finishing the feeding before the bypass feeding flow does not reach stable state, which leads to inaccurate measuring.
Another cause of inaccurate measuring is variation of feeding rate because the variation may make the pre-set amount improper due to its fixed value estimated before starting.
The object of the invention is to provide a controlling apparatus and a controlling method of materials to maintain good accuracy specially in the case where the feeding rate is varied and/or the intended amount is very small.
To accomplish the object, method for controlling a feeding amount of material of the invention to obtain an intended amount of material with high accuracy comprises steps of: detecting a feeding rate; calculating a total fed amount based on the detected feeding rate; shifting the feeding rate from high to low when the total fed amount reaches a value of difference between the intended amount and the alerting amount; calculating a preset amount based on the detected feeding rate and delay time of stopping means to stop feeding the material; and generating a signal to work the stopping means when the calculated total fed amount reaches a value of difference between the intended amount and the preset amount.
A feeding amount controlling apparatus of the invention to obtain an intended amount of material with high accuracy comprises feeding means for feeding a material; feeding rate detecting means for detecting feeding rate of the material; total fed amount calculating means for calculating current total fed amount; stopping means for stopping feeding the material; preset amount calculating means for calculating preset amount by multiply current feeding rate detected by the feeding rate detecting means and delay time together defined as a time from generating a signal for working the stopping means to stopping the feeding completely ;and controlling means for generating the signal to work the stopping means when total fed amount reaches a value defined as the difference between the intended amount to be measured and the preset amount.
It is preferable that the feeding means has feeding rate changing mechanism and the controlling means generates a signal to change the feeding rate from high feeding rate to low one when the total fed amount reaches a value of difference between the intended amount and a predetermined amount (alerting amount).